Outline

Objective: Auditory brainstem implants (ABI) provide a realistic chance for some hearing rehabilitation in patients with neurofibromatosis type 2. In view of recent technological developments and discussion of ideal site of stimulation, the current prospective study was undertaken to optimize clinical outcome and analyze advantageous as well as critical factors in this respect.

Methods: 18 patients with Neurofibromatosis Type 2 were the focus of this analysis with 19 ABI operations being performed under multi-modality neuro-monitoring. Functional outcome was evaluated at 3 to 6 months intervals by monosyllabic word recognition at audiologic and audio-visual mode (MTPa, MTPav) and by open set speech recognition in the Hochmair sentence test (HSM). Factors investigated for their impact on functional outcome were gender, age, duration of deafness, tumour extension and volume, tumorous nerve changes, related paresis and brainstem deformation.

Results: Functional results were available for 16 ABI implantations as two patients had no hearing sensation and one died due to other tumour progression. Four patients achieved very good open speech understanding (HSM 60% to 99%), 3 patients had some open set understanding (10% to 28%), 6 patients had very useful understanding with lip-reading (MTPav 100%). No auditory perception occurred after radiation and in an anatomic variant. Correlation analysis showed that neither patients’ ages nor tumour volume exerted any negative influences. A significant impact on hearing quality was identified for duration of deafness up to one year and for the number of active electrodes where less than 6 electrodes were never associated with open set audiologic understanding.

Conclusions: Different to other reports, this study did not identify severe brainstem compression as a negative predictor, but demonstrated that also patients with previous bilateral severe brainstem compression and large tumor volumes do experience very favourable auditory results. Factors such as functional intra-operative implant placing and short periods of deafness are more relevant than tumour size.